Java：使用 currentTimeMillis() 获取时间很长，如何以 X 小数位精度输出它？
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Java: Getting time with currentTimeMillis() as a long, how do I output it with X decimal place accuracy?
提问by KRB
I have a long that represents System.currentTimeMillis(). I then took another measurement of the time into a long var later in my code. I subtracted the two but now want to see that time to 3 decimal places.
我有一个代表System.currentTimeMillis(). 然后，我稍后在我的代码中将另一个时间测量值转换为 long var。我减去了两个但现在想看到那个时间到小数点后三位。
Currently I use %dto format my output when printing the long var and get only non-decimal values.
目前，我%d在打印 long var 时使用格式化输出并仅获取非十进制值。
回答by Peter Lawrey
longis a whole number. It doesn't have decimal places. Do you mean you want to see seconds to three decimal places?
long是一个整数。它没有小数位。你的意思是你想看到秒到小数点后三位？
long start = System.currentTimeMillis();
long time = System.currentTimeMillis() - start;
System.out.printf("Took %.3f%n", time/1e3);
You can do the same with nanoTime, but it is still a whole number. If you want to see decimal places you need to divide by 1e3 (micro-seconds) or 1e6 (milli-seconds) or 1e9 (seconds)
你可以用 nanoTime 做同样的事情，但它仍然是一个整数。如果要查看小数位，则需要除以 1e3（微秒）或 1e6（毫秒）或 1e9（秒）
回答by Amir Raminfar
You need to divide the number by 1000.0and then display it using "%.3f". So something like
您需要将数字除以1000.0，然后使用"%.3f". 所以像
String.format("%.3f", number / 1000.0)
You need to divide by a doublebecause you want a double. If you did divide by an intthen it would round to the nearest int. You can't use %dbecause it is only used for displaying integers. You have to use %ffor floats and doubles.
你需要除以 adouble因为你想要一个双倍。如果你确实除以 anint那么它会四舍五入到最近的 int。您不能使用，%d因为它仅用于显示整数。你必须使用%f浮动和双打。
